The invention relates to test apparatus for verifying the conformity of a device under test with a standard protocol.
Many standard and proprietary interfaces for electronic communication exist, for example the parallel bus communication within any personal computer, the RS232 serial interface, wireless communication channels and so forth. Each is characterised by a communication protocol defining voltage levels, pulse timings, arbitration, encrypting and/or error correcting algorithms and so forth, to ensure that devices can reliably exchange information (messages).
It is important to verify that a new device using the protocol conforms fully with the protocol to the extent that it is defined. For "low-level" communications protocols such as the RS232 interface, this is a relatively simple matter of timing and level measurements. Moreover, standard chips are available to implement such protocols and when these are incorporated into a device, conformity with the standard can be taken for granted.
A different scale of verification problem arises however when the protocol defines not only how messages are passed, but also the meanings of the messages, rules for when and where the messages are applicable, and the behaviour of the device in response to these messages. A high-level, so-called "application protocol" is presently desired, for example, to extend the IEC standard for the Domestic Digital Bus (D2B) to allow the flexible interconnection of consumer audio/video equipment and other systems. Verifying conformity with a high-level application protocol is not easy because many different device types and configurations may be allowed, with special protocols for each, and many different message formats may be defined.
Moreover, the application protocol may provide rules by which different devices cooperate over an extended time period to achieve a desired result. Protocols by which a number of domestic audio/video apparatuses can cooperate via a D2B bus to identify a signal path are described for example in GB-2 223 114-A (PHN 12678). Protocols by which updated status information can be transmitted automatically by a device are described for example in our United Kingdom patent application 9113793.5 copending with the United Kingdom patent application from which this application claims the benefit of priority (PHQ 91019). The distributed control nature of the D2B system in particular allows distribution of control intelligence through all devices of the system, in contrast to other protocols where there is a clear master-slave relationship between devices.
At the same time, the need for a comprehensive and reliable verification of conformity is absolute in such a field, since many independent manufacturers may be producing devices of many different types for use in an integrated system, while acceptance of the system into the market place depends entirely on consumer confidence in the true inter-brand compatibility of these devices.